From left, Andrew Meas, Dustin Shillcox, Kent Stephenson and Rob Summers are the first to undergo task-specific training with epidural stimulation. / University of Louisville

by Karen Weintraub, Special for USA TODAY

by Karen Weintraub, Special for USA TODAY

Paralysis may not last forever anymore. In an experiment hailed as "staggering," a team of researchers at the University of Louisville and the University of California-Los Angeles restored some voluntary movement to four men who were told they would never move their legs again.

The finding, published online today by the journal Brain, upends understanding of the spinal cord and is likely to transform the lives of more than 1.2 million Americans who lack control over their lower limbs.

"The message here is that patients with spinal cord injury may no longer necessarily say it's a sentence of complete, permanent paralysis," said Roderic Pettigrew, director of the National Institute of Biomedical Imaging and Bioengineering, the federal agency that helped fund the research. "Spinal cord injury is devastating, but now there is hope."

By coursing an electrical current through the four men's spines, the research team, which included scientists from the Pavlov Institute of Physiology in Russia, appears to have "dialed up" signals between the brain and legs that were believed to have been completely lost.

All four men, after being paralyzed for two to four years, can lift their legs, flex their ankles and support their own weight while standing, though only when the device embedded under their skin is turned on.

In a response that shocked researchers, all four have regained bladder and bowel control, sexual function and the ability to regulate their blood pressure and body temperature â?? even when the epidural stimulation device is not running.

It's those seemingly simple improvements that Kent Stephenson says have given him his life back.

"At the age of 22, my doctors were telling me, 'Here's a wheelchair, get used to it,' " said Stephenson of Mount Pleasant, Texas, who was paralyzed from the neck down in a motocross accident in 2009. "(Now) I feel like I'm better than I was. I don't feel like I'm going backwards anymore. ... I can pursue something in life."

Stephenson was the second to receive epidural stimulation. The first patient, Rob Summers, received a lot of attention in 2011 when the record of his stunning recovery was published. Claudia Angeli, an assistant professor at the University of Louisville's Kentucky Spinal Cord Injury Research Center, said no one was sure whether it was a fluke.

Angeli, a biomechanics expert, said she didn't expect Stephenson would respond nearly as well to the epidural stimulation, because he had no feeling at all below his midback injury, while Summers, injured at the neck, had a little.

The day Stephenson was going to be asked to try moving his legs for the first time, they prepared for a long, boring series of tests like others he'd been through seemingly hundreds of times before. Angeli said she expected to ask him many times that day to lift his leg and nothing would happen.

Hooked up to the machine and given the command, Stephenson surprised everyone by voluntarily raising his left leg from the bed.

"I felt a charge go up my leg," he said. "It was unreal. I'd always been told I'd never do that again. My mom busted into tears. I was kind of crying, too."

Angeli admits that she and others spent some time "jumping around the lab" in joy.

The full benefits of epidural stimulation aren't immediate. All four men had to move to Louisville for two years of costly treatment, rehabilitation and experiments. It's too soon to know whether everyone with a spinal cord injury will improve as much as they have, but, as Angeli notes, "with four out of four, it's a very good sign."

The team has begun recruiting a second group of four from among 2,000 volunteers in its database.

The mere fact that the treatment works at all will promote other research in the field, said John Donoghue, a neuroscientist and director of the Brown University Institute for Brain Science, who was not involved in the work.

Scientists have always known that the spinal cord can take over action on its own without help from the brain: Think of how quickly you can right yourself when you trip and how a chicken can keep running around even without its head.

Scientists weren't sure how much of a signal had to reach from the brain down the spinal cord to trigger the initial action. Now they know a very weak signal may be enough, said Donoghue, who works with Veterans Affairs.

"This could open up a whole new set of ideas of how you could treat spinal cord injury," he said.

There's no question that the success of epidural stimulation will benefit other people with paralysis, said Peter T. Wilderotter, president and CEO of the Christopher and Dana Reeve Foundation, which raises money for spinal cord research and helped fund the study.

"The changes we see here are really staggering," he said. "It's truly a breakthrough. It means extraordinary hope and a change in their whole quality of life and what they can look forward to."